Engineering topics

Phillips, J. L.

Publications and source records attributed to Phillips, J. L..

At least 73 records · Page 4

NASA NTRS1992

The Ulysses solar wind plasma investigation - Experiment description and initial in-ecliptic results

During the in-ecliptic flight of Ulysses from the Earth toward its encounter with Jupiter, the Los Alamos solar wind plasma experiment has performed well. Briefly described, the instrumentation contains two independent electrostatic analyzers, one for ions and one for electrons. Initial analysis of solar wind electron core temperatures obtained between 1.15 and 3.76 AU yields a gradient of T (proportional to) R(exp -0.7) which is flatter than expected for adiabatic expansion of a single-temperature Maxwellian velocity distribution and steeper than that obtained from Mariner-Voyager.

Bame, S. J.↗

NASA NTRS1992

Disconnection of open coronal magnetic structures

We have examined the Solar Maximum Mission coronagraph/polarimeter observations for evidence of magnetic disconnection of previously open magnetic structures and a number of likely examples have been found. Probable coronal disconnections typically appear as pinching off of helmet streamers followed by the release and outward acceleration of a large U or V-shaped structure. The observed sequence of events is consistent with reconnection across the heliospheric current sheet between previously open magnetic field regions, and the creation of a detached magnetic structure which is open to interplanetary space at both ends. Sunward of the reconnection point, coronal disconnection events would return previously open magnetic flux to the Sun as closed field arches. Here we (1) describe one clear disconnection event (1 June 1989); (2) examine the results of a limited survey of disconnection events; and (3) discuss the potential importance of coronal disconnections for maintaining flux in interplanetary space.

Mccomas, D. J.↗

NASA NTRS1992

Counterstreaming solar wind halo electron events on open field lines?

Counterstreaming solar wind halo electron events have been identified as a common 1 AU signature of coronal mass ejection events, and have generally been interpreted as indicative of closed magnetic field topologies, i.e., magnetic loops or flux ropes rooted at both ends in the Sun, or detached plasmoids. In this paper we examine the possibility that these events may instead occur preferentially on open field lines, and that counterstreaming results from reflection or injection behind interplanetary shocks or from mirroring from regions of compressed magnetic field farther out in the heliosphere. We conclude that neither of these suggested sources of counterstreaming electron beams is viable and that the best interpretation of observed counterstreaming electron events in the solar wind remains that of passage of closed field structures.

Gosling, J. T.↗

NASA NTRS1992

Regulation of the interplanetary magnetic field

In this study we use a recently developed technique for measuring the combined magnitudes of inward and outward (sunward and antisunward) pointing 2D magnetic flux in the ecliptic plane to examine (1) the long term variation of the amount of magnetic field open to interplanetary space and (2) the apparent rate at which coronal mass ejections (CMEs) may be opening new magnetic field from the sun. Since there is a substantial variation (about 50 percent) of these combined fluxes in the ecliptic plane over solar cycle 21, we conclude that there must be some means whereby new field can be opened from the sun and a previously open magnetic field can be closed off. We briefly describe recently discovered coronal disconnection events which could serve to close off a previously open magnetic field. CMEs appear to retain at least partial magnetic connection to the sun and hence open up a new field, while disconnections appear to be likely signatures of the process that returns a closed field to the sun. The combination of these processes could regulate the amount of inward and outward magnetic flux open to interplanetary space.

Mccomas, D. J.↗

NASA NTRS1992

Quantitative analysis of bidirectional electron fluxes within coronal mass ejections at 1 AU

The solar wind electron heat flux is carried primarily by suprathermal electrons beamed antisunward along the interplanetary magnetic field. However, analysis of electron observations at 1 AU has shown that counterstreaming electron beams, suggesting closed magnetic structures, prevail within coronal mass ejections (CMEs). These structures might be magnetic 'tongues', magnetically detached plasmoids, or complex flux ropes. Here we show results of analysis of ISEE-3 observations within 39 CMEs, including the asymmetry between the two beams, its control by magnetic field orientation, and the variation of the electron distributions as CMEs convect past the spacecraft. We find that some CMEs are strongly asymmetric, with the antisunward beam generally dominant, while others contain nearly symmetric beams. The beam asymmetries, and the magnetic field orientations, exhibit characteristic trends as CMEs pass over the spacecraft. We present an example of a distinctive 'strahl-on-strahl' distribution, suggesting continued magnetic connection to the corona, in which a narrow antisunward beam is superimposed on a broader beam. Our results favor continuing magnetic connection to the Sun in a tongue or flux rope geometry rather than a fully detached plasmoid.

Phillips, J. L.↗

NASA NTRS1991

Wave mode identification of electrostatic noise observed with ISEE 3 in the deep tail boundary layer

The characteristics of the VLF electrostatic noise observed with ISEE 3 in the low-latitude boundary layer of distant geomagnetic tail are examined using a display format for the wave dynamic spectra different from that used by Scarf et al. (1984). It is shown that the observed noise is composed of impulsive bursts. The results of the detailed analysis of the noise parameters are used to develop a model of plasma wave behavior in the plasma rest frame. A hypothesis is proposed that the wide frequency extent of the noise spectra is composed of Doppler effects of waves propagating nearly omnidirectionally within the plasma rest frame, which is moving with the electron bulk speed. On the basis of this hypothesis, the wavelength of the observed waves were determined from the width of the frequency extent and the measured electron bulk speed. It is shown that the wavelength ranges from 2 to 8 times the plasma Debye length.

Tsutsui, M.↗

NASA NTRS1991

Geomagnetic activity associated with earth passage of interplanetary shock disturbances and coronal mass ejections

Coronal mass ejection events (CMEs) are important occasional sources of plasma and magnetic field in the solar wind at 1 AU, accounting for approximately 10 percent of all solar wind measurements in the ecliptic plane during the last solar activity maximum. Using a recently appreciated capability for distinguishing CMEs in solar wind data in the form of counterstreaming solar wind electron events, this paper explores the overall effectiveness of shock wave disturbances and CMFs in general in stimulating geomagnetic activity. The study is confined to the interval from mid-August 1978 through mid-October 1982, spanning the last solar activity maximum, when ISEE 3 was in orbit about the L1 Lagrange point 220 Re upstream from earth. It is found that all but one of the 37 largest geomagnetic storms in that era were associated with earth passage of CMEs and/or shock disturbances, with the large majority of these storms (27 out of 37) being associated with interplanetary events where earth encountered both a shock and the CME driving the shock (shock/CME events). Although CMEs and/or shock disturbances were increasingly the cause of geomagnetic activity as the level of geomagnetic activity increased, many smaller geomagnetic disturbances were unrelated to these events.

Gosling, J. T.↗

NASA NTRS1991

The 1983 tail-era series. Volume 1: ISEE 3 plasma

Observations from the ISEE 3 electron analyzer are presented in plots. Electrons were measured in 15 continuous energy levels between 8.5 and 1140 eV during individual 3-sec spacecraft spins. Times associated with each data point are the beginning time of the 3 sec data collection interval. Moments calculated from the measured distribution function are shown as density, temperature, velocity, and velocity azimuthal angle. Spacecraft ephemeris is shown at the bottom in GSE and GSM coordinates in units of Earth radii, with vertical ticks on the time axis corresponding to the printed positions.

Fairfield, D. H.↗

NASA NTRS1991

Observations of disconnection of open coronal magnetic structures

The solar maximum mission coronagraph/polarimeter observations are surveyed for evidence of magnetic disconnection of previously open magnetic structures and several sequences of images consistent with this interpretation are identified. Such disconnection occurs when open field lines above helmet streamers reconnect, in contrast to previously suggested disconnections of CMEs into closed plasmoids. In this paper a clear example of open field disconnection is shown in detail. The event, on June 27, 1988, is preceded by compression of a preexisting helmet streamer and the open coronal field around it. The compressed helmet streamer and surrounding open field region detach in a large U-shaped structure which subsequently accelerates outward from the sun. The observed sequence of events is consistent with reconnection across the heliospheric current sheet and the creation of a detached U-shaped magnetic structure. Unlike CMEs, which may open new magnetic flux into interplanetary space, this process could serve to close off previously open flux, perhaps helping to maintain the roughly constant amount of open magnetic flux observed in interplanetary space.

Mccomas, D. J.↗

NASA NTRS1990

Coronal mass ejections and large geomagnetic storms

Previous work indicates that coronal mass ejection (CME) events in the solar wind at 1 AU can be identified by the presence of a flux of counterstreaming solar wind halo electrons (above about 80 eV). Using this technique to identify CMEs in 1 AU plasma data, it is found that most large geomagnetic storms during the interval surrounding the last solar maximum (August 1978 - October 1982) were associated with earth-passage of interplanetary disturbances in which the earth encountered both a shock and the CME driving the shock. However, only about one CME in six encountered by earth was effective in causing a large geomagnetic storm. Slow CMEs which did not interact strongly with the ambient solar wind ahead were particularly ineffective in a geomagnetic sense.

Gosling, J. T.↗

NASA NTRS1990

Radial evolution of solar wind thermal electron distributions due to expansion and collisions

ISEE 3 electron observations near 1 AU show that the solar wind thermal electron temperature anisotropy, T(parallel)/T(perpendicular), is typically 1.0 to 1.5, with densest distributions most nearly isotropic, but is sometimes much higher when density is low. For a small observational subset characterized by high density and low bulk speed, T(perpendicular) can exceed T(parallel). Based on these and other observations, a simple model is proposed for radial evolution of thermal electrons in a structureless solar wind under the influence of Coulomb collisions and geometric expansion in a spiral interplanetary magnetic field. The model, which satisfactorily explains the 1 AU observations, shows that the evolution of electron temperature and T(parallel)/T(perpendicular) is controlled by plasma density, flow speed, and initial temperature, with density the most important factor. The model makes predictions for radial distances other than 1 AU and for high solar latitudes.

Phillips, J. L.↗

NASA NTRS1990

The 1983 tail-era data series. Volume 2: ISEE 3 magnetic field

ISEE 3 spacecraft measurements within and near the Earth's magnetic tail is presented. Plots are shown of ISEE 3 magnetic field data. The plots in this volume showing observations from the ISEE 3 vector helium magnetometer experiment were produced from a tape of merged plasma/magnetic field data. The magnetometer produced six vector measurements/sec that were subsequently averaged over one minute intervals before merging with plasma data. Merging was accomplished by associating the nearest 1 minute field average with each plasma sample.

Fairfield, D. H.↗

NASA NTRS1990

The Ashen Light

Present understanding of the Ashen Light of Venus is reviewed. Ashen Light is most often reported when Venus is in the evening sky, when the evening terminator of Venus is toward the earth. It is argued that the local time asymmetry is too great to be explained by terrestrial effects alone. It is argued that Venus lightning is the only known phenomenon that shows a marked dawn-dusk asymmetry on Venus and which could also explain the occurrence of Ashen Light. The following factors appear to affect the visibility of Ashen Light from earth: the distance of Venus from the earth, the length of time Venus is above the horizon, and the local time distribution of the Ashen Light source on Venus.

Russell, C. T.↗

NASA NTRS1989

ISEE 3 observations of solar wind thermal electrons with T-perpendicular greater than T-parallel

This study presents ISEE 3 observations of anomalous electron distributions for which T-perpendicular exceeds T-parallel in the solar wind near 1 AU. Twelve anomaly events were identified, lasting from 24 min to 6 hours. These events generally share the following characteristics: (1) high plasma density, (2) low solar wind speed, (3) magnetic field which is nearly transverse to the flow, and (4) low electron and ion temperatures. The processes of solar wind adiabatic expansion and isotropization via Coulomb collisions could be expected to lead to such anomalous anisotropies under conditions similar to those observed. However, these conditions actually produce T-perpendicular greater than T-parallel for only a small fraction of the time, suggesting that other mechanisms are also important in regulating solar wind electron distributions.

Phillips, J. L.↗

NASA NTRS1989

Anisotropic thermal electron distributions in the solar wind

This paper presents data on ISEE 3 observations of unusually anisotropic core electrons detected in the solar wind near 1 AU, which exhibited temperature (T) ratios T-parallel/T-perpendicular of 1.5 to 4. Distinct anisotropy events are described, together with the observed correlations between core temperature anisotropy and various other solar wind parameters. It was found that the periods of extreme electron anisotropy tended to be coincident with intervals of double ion beam, suggesting similar causal mechanisms for the two phenomena.

Phillips, J. L.↗

NASA NTRS1989

Electron heat flux dropouts in the solar wind - Evidence for interplanetary magnetic field reconnection?

An examination of ISEE-3 data from 1978 reveal 25 electron heat flux dropout events ranging in duration from 20 min to over 11 hours. The heat flux dropouts are found to occur in association with high plasma densities, low plasma velocities, low ion and electron temperatures, and low magnetic field magnitudes. It is suggested that the heat flux dropout intervals may indicate that the spacecraft is sampling plasma regimes which are magnetically disconnected from the sun and instead are connected to the outer heliosphere at both ends.

Mccomas, D. J.↗

NASA NTRS1988

Asymmetries in the location of the Venus ionopause

Four large data sets of Venus ionopause observations, based on different definitions and observations by Pioneer Venus Orbiter field and particle instruments, are compared. Regardless of the definition chosen, the ionopause is observed to be higher on average at dawn than at dusk. The results of an empirical ionosphere model and a data analysis technique which minimizes orbital bias are combined to show that most or all of this asymmetry results from the effects of orbital bias and uneven sampling of solar wind conditions. However, an additional asymmetry is found in which the ionopause is displaced in the direction opposite to the motional electric field of the solar wind. This effect is attributed to asymmetric pickup of exospheric ions by the electric and magnetic fields in the magnetosheath. This ion pickup interpretation can be understood in terms of a previous observed magnetosheath magnetic field asymmetry. Quantitative analysis indicates that the transverse momentum imparted by the solar plasma to pickup particles in their initial gyration is transmitted by the magnetosheath magnetic field to the ionosphere boundary.

Phillips, J. L.↗

NASA NTRS1987

Effect of possible passage through Halley's magnetic tail on geomagnetic activity

It is found that there occurred a geomagnetic storm on May 18/19, 1910 that cannot be dismissed as a recurrent storm. The period of storminess is close to the period of time at which the magnetic and plasma tail of Halley should have passed over the earth. The signature is worldwide and of the form and magnitude expected if the solar wind were shielded from the earth by the comet. Comparison with computer simulations applicable closer to the comet suggests that this interpretation is feasible. If this interpretation is correct, the 'lobes' of the Halley tail have deeper lows at 24 x 10 to the 6th km than in the present model at 7 x 10 to the 6th km downstream and are at least twice as wide.

Russell, C. T.↗